[jedberg]

AWS makes it pretty easy to operate in multiple AZs within a region (each AZ is considered a separate datacenter but in real life each AZ is multiple datacenters that are really close to each other).

That being said, there is still an added cost and complexity to operate in multiple AZs, because you have to synchronize data across the AZs. Also you have to have enough reserved instances to move into when you lose an AZ, because if you're running lean and each zone is serving 33% of your traffic, suddenly the two that are left need to serve 50% each.

The bigger companies with overhead reservations will get all the instances before you can launch any on demand during an AZ failure.

[Tehnix]

> each AZ is considered a separate datacenter but in real life each AZ is multiple datacenters that are really close to each other

For AWS specifically, I’m fairly certain they maintain a minimum distance and are much more strict on requirements to be on different grids etc than other Cloud providers. A few years ago they were calling out Azure and Google Cloud on exactly what you describe (having data centers essentially on the same street almost).

[jedberg]

A single AZ may have neighboring datacenters, but they are very strict on having datacenters for different AZs be at least 100km apart and on different flood plains and power grids.

[laluser]

This should be at most 100km. Range is in 60km-100km range typically.

[throwbigdata]

100km? Oh really?

[throwbigdata]

https://docs.aws.amazon.com/sap/latest/general/arch-guide-ar...

Each Availability Zone can be multiple data centers.At full scale, it can contain hundreds of thousands of servers. They are fully isolated partitions of the AWS global infrastructure. With its own powerful infrastructure, an Availability Zone is physically separated from any other zones. There is a distance of several kilometers, although all are within 100 km (60 miles of each other).

[eurleif]

So at most 100km, not at least 100km.

[dodobirdlord]

I think you may have slightly misread. I think what’s being said is that a single logical AZ may actually be multiple physical datacenters in close proximity.

[mediascreen]

At least in eu-north-1 the three AZs are located in different towns, about 50 km apart (Västerås, Eskilstuna and Katrineholm).